We follow a simple rule about technical debt:

If you are working on an issue, and technical debt is affecting your ability to create factored, testable code, then fix the debt.

It might mean a 1 hour issue takes 4 hours, or more. But we put a premium on writing tested code, such that we can push builds often to production.

However, we never make a task ' go fix technical debt X'.

That way, you don't waste time on something that really isn't a problem.

It's working for us well, so far.